1. Field of the Invention
The present invention relates to an RFID (Radio Frequency IDentification) tag which exchanges information with external equipment in a non-contact manner and relates to its manufacturing method. Incidentally, the “RFID tag” used in the present specification is also called as an “RFID tag inlay” among those skilled in the art, meaning an internal constituent part (inlay) used in the “RFID tag”. In addition, the “RFID tags” include a contactless IC card.
2. Description of the Related Art
In recent years, various types of RFID tag have been proposed to exchange information with external equipment typified by reader-writers in a non-contact manner by radio (see, for example, Japanese Patent Application Publication Nos. 2000-311226, 2000-200322, 2001-351082).
As a type of RFID tag, there has been proposed a configuration in which an antenna pattern for wireless communications and an IC chip are mounted on a base sheet made of plastics or paper. One possible application for RFID tags of this type is to affix them to goods and identify the goods by exchanging information about the goods with external equipment.
FIG. 1 is a schematic cross-sectional view showing an example of RFID tags of this type.
An RFID tag 10 shown here has an antenna 12 formed of a conductive pattern on a sheet type base 11 and a circuit chip 13 mounted thereon. A circuit for exchanging information with external equipment via the antenna 12 is incorporated into the circuit chip 13. Connection terminals 13a formed on the lower surface of the circuit chip 13 are electrically connected to two mounting pads of the antenna 12 (to be described later), which are formed to be close to each other, by soldering or the like, and each of their surroundings is fixed to the base 11 with an adhesive 14.
Potential use of RFID tags has spread extremely widely and one important factor to actualize the use is how to reduce the manufacturing cost and achieve mass production at low cost.
Arrangement of connection terminals of the circuit chip is one condition that contributes to allowing mass production to reduce the cost of products. When the connection terminals are arranged in such a way that the circuit chip must be directed in a specific direction to be electrically connected to antenna terminals, postures of the circuit chip must be precisely controlled one by one at the time of connection. This may be an impediment to improvement in productivity.
FIG. 2 is a diagram showing a first example of connection terminals formed on the lower surface of the circuit chip.
FIG. 2 shows a square circuit chip 13A. At four corners of the lower surface of the square circuit chip 13A, each of four terminals in total is formed, which is connected to one of two mounting pads 121 and 122 (see FIG. 3) to be described later.
In this case, among the four terminals, two terminals 131 of one diagonal are antenna terminals that are connected to an electronic circuit in the circuit chip 13A to provide an electrical connection to an antenna 12 (see FIG. 1). The other two terminals of the other diagonal are dummy terminals that are non-connected to the electronic circuit in the circuit chip 13A and that aim to improve stabilization of the posture of the circuit chip 13A when the circuit chip 13A is mounted.
FIG. 3 is a diagram showing a positional relationship between the mounting pads and the circuit chip.
Although FIG. 3 shows two mounting pads 121 and 122, these two mounting pads 121 and 122 correspond to two end sections of the antenna 12 shown in FIG. 1, which are positioned at the circuit chip 13 sides and arranged close to each other.
Now, in the structure in which two antenna terminals 131 of one diagonal and two dummy terminals 132 of the other diagonal are formed in the square circuit 13A as shown in FIG. 2. The circuit chip 13A may be disposed in a positional relationship with respect to the mounting pads 121 and 122 as shown in FIG. 3, and may be rotated about a central point O of the circuit chip 13A by any angle of 90 degrees, 180 degrees and 270 degrees in the direction of an arrow from the positional relationship shown in FIG. 3. In any of these arrangements, one of two antenna terminals 131 and 132 is connected to one of two mounting pads 121 and 122, and the other antenna is connected to the other mounting pad. Accordingly, even when the circuit chip is connected to the mounting pad at any rotation position, the normal operation as the RFID tag can be expected.
In other words, this terminal arrangement eliminates the need for considering the direction of the circuit chip in mounting the circuit chip on the mounting pads, and is expected to simplify mounting equipment and achieve high-speed mounting.
However, depending on the configuration, the layout and the like of the electronic circuit in the circuit chip, the antenna terminals 131 of one diagonal and the dummy terminals 132 of the other diagonal cannot be always arranged as shown in FIG. 2. In some cases, the terminals may be arranged as shown in FIG. 4 to be explained below.
FIG. 4 is a diagram showing a second example of a terminal arrangement of the lower surface of the circuit chip.
Similar to the circuit chip 13A in FIG. 2, FIG. 4 shows a square circuit chip 13B, however, the terminal arrangement differs from that of the circuit chip 13A in FIG. 13A. Specifically, each of four terminals in total is formed at one of four corners of the lower surface of the circuit chip 13B. However, among the four terminals, each of two antennas terminals 131 in total is formed at one of two corners along one side 139 of the lower surface of the circuit chip 13B and the remaining two terminals are formed as dummy terminals 132.
The circuit chip 13b having this terminal arrangement is assumed to be rotated by 90 degrees, 180 degrees and 270 degrees.
FIG. 5 is a diagram showing the positional relationship between the mounting pads and the circuit chip 13B having the terminal arrangement shown in FIG. 4.
Part (A) of FIG. 5 shows a state in which the circuit chip 13B shown in FIG. 4 is formed on the mounting pads 121 and 122 with the posture shown in FIG. 4 unchanged. In each of parts (B) to (D) of FIG. 5, a state is shown in which the circuit chip 13B is rotated about a central point O of the circuit chip 13B by each of 90 degrees, 180 degrees and 270 degrees in the direction of an arrow from the posture shown in part (A) of FIG. 5.
As is obvious from parts (B) to (D) of FIG. 5, no problem occurs in the cases of parts (A) and (C) of FIG. 5 since one and the other mounting pads 121 and 122 are formed on one and the other antenna terminals 131, respectively. In the cases of parts (B) and (D) of FIG. 5, both of two antenna terminals 131 are formed on only one of two mounting pads 121 and 122, and the normal operation as the RFID tag cannot be performed if nothing is done.
In other words, in the case of combinations of the circuit chip 13B having the terminal arrangement shown in FIG. 4 and the mounting pads 121 and 122, there is a need to accurately manage postures of the circuit chip 13B in the rotation direction one by one when the circuit chip 13B is mounted, resulting in a large reduction in production efficiency, which causes serious impediments to mass production and cost reduction.
In order to solve this problem, the following technique is proposed in Japanese Patent Application Publication No. 2005-107882.
FIG. 6 is a diagram showing a terminal arrangement of a circuit chip proposed in Japanese Patent Application Publication No. 2005-107882.
A circuit 13C shown in FIG. 6 also has a square shape, however, dummy terminals are not formed unlike those shown in FIGS. 2 and 4, and all of four terminals formed at four corners are antenna terminals connected to the internal circuit. It is noted that two antenna terminals 131a formed at two corners along one side 139a of the lower surface of the circuit chip 13C are connected to each other on the internal circuit, while two antenna terminals 131b formed at two corners along another one side 139b are also connected to each other on the internal circuit.
In Japanese Patent Application Publication No. 2005-107882, various ideas are added to the shape of the mounting pads.
FIG. 7 is a diagram showing a state in which a circuit chip having the terminal arrangement shown in FIG. 6 is formed on mounting pads each having a shape proposed in Japanese Patent Application Publication No. 2005-107882.
Pads 121′ and 122′ shown in FIG. 7 are shaped to be connected to only any one of four terminals formed at four corners of the circuit chip 13C.
Part (A) of FIG. 7 shows a state in which the circuit chip 13C shown in FIG. 6 is formed on the mounting pads 121′ and 122′ with the posture shown in FIG. 6 unchanged. In each of parts (B) to (D) of FIG. 7, a state is shown in which the circuit chip 13C is rotated about a central point O of the circuit chip 13C by each of 90 degrees, 180 degrees and 270 degrees in the direction of an arrow from the posture shown in part (A) in FIG. 7.
According to the circuit chip 13C having the terminal arrangement shown in FIG. 6 and the mounting pads 121′ and 122′ each having a shape shown in FIG. 7, one and the other mounting pads 121′ and 122′ are formed on one and the other antenna terminals 131a and 131b, respectively, regardless of the rotation state of the circuit chip 13C. Therefore, it is possible to connect the circuit chip 13C to the mounting pads 121′ and 122′ without considering the rotation of the circuit chip 13C, which is expected to simplify mounting equipment and achieve high-speed mounting.
However, in the case of the proposal of Japanese Patent Application Publication No. 2005-107882 shown in FIGS. 6 and 7, although four terminals are formed at four corners of the lower surface of the circuit chip 13C, respectively, only two terminals contribute to mounting while other two terminals do not contribute to mounting. Despite provision of dummy terminals in the circuit chips 13A and 13B shown in FIGS. 2 and 4 to improve stabilization when they are mounted, variations in position and posture caused in mounting are largely increased, so that performance of the RFID tag may vary greatly.
Moreover, in the circuit chip 13C shown in FIG. 6, although two terminals each are electrically connected to each other in the internal circuit, such connection originally allows the use of only terminals of one diagonal as antenna terminals and terminals of the other diagonal as dummy terminals as shown in FIG. 2. In this case, all four terminals formed at four corners are used for connection without considering the rotation position of the circuit chip as shown in FIG. 3, which makes it possible to improve stabilization of the circuit chip when the circuit chip is mounted, and therefore there are no merits in the configurations as in FIGS. 6 and 7.